Review and Measurements of Meier Corda Jazz Amp

[Silou]

Someone else measured the device and the results are comparable, but his analyzer does not seem that capable http://mclements.net/Mike/mrc-blog/blog-140615.html

 

[Deleted member 2944]

Amir noted the crossfeed function was disabled, so any L/R issues should be eliminated.
With his analyzer in floating mode, any grounding of active signal issues should be eliminated also.

It sure looks like simply a poor performing product.

Dave.

 

[elira]

I listened to the headphone. It clearly lacks power and gets distorted precisely the way the measurements predict. There simply is not four times the amount of power available.

It could be confirmation bias, your strong beliefs in the measurements trick your mind to hear distortion.

 

[Veri]

Amir noted the crossfeed function was disabled, so any L/R issues should be eliminated.
With his analyzer in floating mode, any grounding of active signal issues should be eliminated also.

It sure looks like simply a poor performing product.

Dave.

Unfortunately so. What a shame! I now have doubts his new expensive flagship will be all that better.

 

[Veri]

It could be confirmation bias, your strong beliefs in the measurements trick your mind to hear distortion.

There is placebo effect and there is not driving the hd650 before they start to sound like ass

The 4XX distorting even faster also corresponds with measurement.

 

[amirm]

It could be confirmation bias, your strong beliefs in the measurements trick your mind to hear distortion.

Not this kind of distortion. It is extremely severe just like turning up a clock radio past 12:00.

 

[amirm]

Amir noted the crossfeed function was disabled, so any L/R issues should be eliminated.

FYI I played with the switch and it makes no difference on distortion measurements.

 

[MRC01]

...I did hear that the output is 15 volts which I am NOT seeing. So I buy that there is some kind of inverse signal on ground but bottom line is that my analyzer in floating mode, is measuring what a headphone sees. ...

How does the AP work in floating mode? Does it difference the output ground with the signal? The reason I ask is because reading Meier's description linked above, there's an important difference between this amp and balanced.
If you ignore the - signal (difference the + against earth ground instead of output ground):
A normal balanced signal doesn't mix L & R, so you won't get more distortion, just 6 dB worse power and S/N.
This amp mixes L with inverted L+R on each channel, and the ground carries the inverted L+R which differences it out. So if you don't difference it, you'll measure not only lower power, but also distortion.

He says, "severe distortion passed 12' o clock" no matter if balanced or non-balanced or Jan Meier's balanced mode ......?

I few years ago I measured this amp using an ESI Juil@ sound card, nowhere near as nice as Amir's AP rig. But the Juli@ does have balanced inputs and the only distortion above -90 dB was 60 Hz from the transformer. How much lower was the THD+IMD, I can't tell as it would be masked by the Juli@'s own distortion. But it did have that voltage clipping beyond around 2:00 on the volume knob. That appears to be a design flaw.

 

[MRC01]

Someone else measured the device and the results are comparable, but his analyzer does not seem that capable http://mclements.net/Mike/mrc-blog/blog-140615.html

Yeah, that was me. I confirmed the same IMD voltage clipping that Amir measured when the knob was past the 2:00 position. But at normal volume settings my measurements were cleaner than what Amir measured here. Of course, my equipment was just a sound card so it could be suspect.

During my first try, I measured it as unbalanced and got the same low power & high distortion that Amir measured here. That's why I'm curious whether this unique active-balanced-ground is a factor here.

 

[agjell]

They didn't even get the CE logo right...
https://ce-check.eu/ce-marking-topics/the-ce-mark-of-a-product-real-or-fake/

 

[elira]

@amirm are both of the units normal Corda Jazz?, or is one of them the ff version?

 

[Nango]

They didn't even get the CE logo right...
https://ce-check.eu/ce-marking-topics/the-ce-mark-of-a-product-real-or-fake/

Amaizing.... takes the biscuit!!!!

 

[graz_lag]

No surprise here ...
The unit is marked as "Designed by ... Germany" not "Built by ... in Germany" so you guess where it was built ...

 

[Schackmannen]

@amirm Why does the SNR increase when you measure the amp at 50 mV output vs full output? I thought that a lower output would basically always decrease the SNR all else being equal. I might be calculating this wrong but wouldn't a 90 dB SNR at 50 mV mean that the residual noise is only around 1.5 uV which is very low, almost at the level of the analyzer it self right?

 

[Nango]

No surprise here ...
The unit is marked as "Designed by ... Germany" not "Built by ... in Germany" so you guess where it was built ...

My god I always thought at least such things would have been built in Germany, how innocent........

 

[Nango]

Unfortunately so. What a shame! I now have doubts his new expensive flagship will be all that better.

His flagship you mention is being built by Lake People in their facilities, just in case you didnt know......................

 

[amirm]

How does the AP work in floating mode? Does it difference the output ground with the signal? The reason I ask is because reading Meier's description linked above, there's an important difference between this amp and balanced.
If you ignore the - signal (difference the + against earth ground instead of output ground):
A normal balanced signal doesn't mix L & R, so you won't get more distortion, just 6 dB worse power and S/N.
This amp mixes L with inverted L+R on each channel, and the ground carries the inverted L+R which differences it out. So if you don't difference it, you'll measure not only lower power, but also distortion.

Unbalanced connections are always referenced to the second conductor. In floating unbalanced mode, the AP acts exactly as you need it to do, to measure such a device. It measures the difference between the two wires while keeping the input unconnected to chassis ground.

For grins, I ran the same power test versus distortion using AP's balanced input:

As you see, the results are essentially the same. They would be identical if I could keep the volume control at max as the original test. Using balanced input though, the amp goes nuts above 0.5 volt input (it is already clipping) and won't recover until max input (with severe clipping).

Again, all of this is beside the point. I can clearly hear massive distortion as I turn up the volume on HD-650 which indicates we have entered the clipping point very early. 30 Milliwatts is just not enough power prior to clipping.

For whoever asked for the second unit to be tested, the graph in pink is with the second unit, the one in orange is the first unit. Remeasuring it with floating unbalanced we get identical results:

So whatever is broken in the design exists in both.

 

[elira]

My god I always thought at least such things would have been built in Germany, how innocent........

I remember seeing somewhere that their products were made in China to keep prices low. In fact their website doesn’t say “made in Germany” for the Corda Jazz.

 

[MRC01]

@amirm are both of the units normal Corda Jazz?, or is one of them the ff version?

I think it's one of each. Amir showed one that had the FF, and the other is mine which does not have it.
In case anyone's wondering, FF is essentially frequency emphasis in the internal gain-feedback loop. The amp boosts frequencies from around 100 Hz to 2 kHz (or attenuates freqs outside this range), so this freq range is exaggerated in the internal gain-feedback loop. Then it does the reverse before the output signal leaves the amp, so frequency response remains flat. The idea is to frequency-shape distortion, minimizing it in the critical hearing frequencies. Whether it works in practice, measurements should be able to indicate.

 

[MRC01]

Unbalanced connections are always referenced to the second conductor. In floating unbalanced mode, the AP acts exactly as you need it to do, to measure such a device. It measures the difference between the two wires while keeping the input unconnected to chassis ground.
...
So whatever is broken in the design exists in both.

OK, as I understand how it works, this (balanced inputs) is the correct way to measure it. And that looks bad!
We both saw it go nuts, but at very different points. When I measured it a few years ago, it was clean (nothing above -90 dB) up to about the 2:00 position, which IIRC was at least 2 Vrms. You see both going nuts much lower at 0.5V!

Here's what's suspicious: if the amp works as designed, it will measure very differently with balanced vs. unbalanced. Mine did, when I measured it several years ago. But you're measuring the same either way, balanced or unbalanced. That might suggest both amps have a broken/dead ground channel. Can you measure whether there is a signal on the ground channel? That might resolve this mystery. It's possible the measurement rig shorted and fried the ground channels when they were connected as unbalanced.